Electronic and Vibrational Circular Dichroism Spectra of Chiral 4-X-[2.2]paracyclophanes with X containing Fluorine Atoms

The absorption IR and vibrational circular dichroism (VCD) spectra of both enantiomers of 4-X- [2.2]paracyclophanes (X ) F, CH2F, COCF3) have been recorded in the mid-IR and CH stretching regions. The electronic CD (ECD) spectra have been collected as well. VCD spectra in the two IR regions, 900-1700 cm-1 and 2700-3200 cm-1, have been compared with the corresponding DFT calculated spectra. The absolute configuration assignment was confirmed as previously determined. We have shown that, to various extents, the VCD and ECD spectra bear some information on the relative mobility of the two phenyl rings and on the existence of different conformers for the X group. It has been observed that X ) F and X ) CH2F groups do not change the conformational and electronic properties of the parent X ) H and X ) CH3 molecules. The X ) COCF3 group brings in a large perturbation to the [2.2]paracyclophanes, and the role of fluorine is less important than that of oxygen.